The present invention relates to the art of bonding of plastic films. More specifically, the present invention provides a method and apparatus for ultrasonically bonding thermoplastic photographic film by the application of oscillatory energy applied along a thin line of contact and essentially perpendicular to the overlapped edges of such film. The instant invention encompasses the ultrasonic bonding of all conventional bases for photographic films.
The adaptation of ultrasonic means for the bonding of plastic materials is old and well known in the art. Ultrasonic bonding offers many distinct advantages and improvements, especially for splicing photographic films employing certain types of base materials, such as polyesters which are finding increased professional use, over older known splicing techniques such as by taping and the like. The technique involves placing work members to be joined in an overlapping position and thereafter applying appropriate ultrasonic bonding pressure. It has been noted that the ultrasonic energy applied to the overlapping work pieces is accompanied by a degree of heating which is primarily due to the frictional forces existing between the overlapping surfaces of the work pieces whereby molecular and/or fusion bonding occurs. Needless to say, this technique has been applied to the bonding of photographic film, e.g. celluose triacetate. The December 1961 issue, volume 70, of the "Journal of the Society of Motion Picture and Television Engineers" contains an article at page 976 which discloses an ultrasonic technique for splicing motion picture film. Numerous devices have also been perfected to practice this technique.
A number of photographic film splicers available on the market today utilize a sealing assembly comprising anvil and horn means which define a compression zone in which work pieces are operably positioned for bonding. The horn is generally connected to ultrasonic means whereby oscillatory energy is imparted to the overlapping work pieces confined between the horn and the anvil. In these prior art devices, the oscillatory energy applied to the work pieces confined between the anvil and the horn is applied over the entire width of the compression zone defined between the anvil and the horn. It can be appreciated that where the compression zone is established other than by a small area of contact between such members, then the size of the transducer or driver of the ultrasonic means must be sufficient when energized to thereby vibrate the horn at the requisite ultrasonic bonding frequency as compared to that required in a splicing operation where only a small area of contact between the anvil and the horn is employed. The net result is that a considerable greater power input to the equipment is required.
Another inherent problem in prior art splicers employing an anvil and horn assembly whereby the bonding pressure is applied over a relatively wide area, that is, other than by a small area of contact, is the fact that the anvil and horn members must be carefully aligned whereby essentially uniform pressure is applied over the entire area. Otherwise, it has been observed that an uneven application of the oscillatory energy tends to cause burning of the film strips in the area of the highest clamping pressure, and in any event, the low pressure area may not even receive sufficient energy to achieve a splice or bond in that area. Thus, to achieve a satisfactory ultrasonic film splice, the clamping pressure must be applied uniformly. Moreover, even if the clamping pressure is not excessive to the extent that burning does not occur, warping or interference with the sound track quite often imparted to the edge of the film may occur. The net result is the fact that such prior art ultrasonic splicers generally cost more to produce due to the manufacturing tolerances that must be met in their manufacture as a primary factor of the alignment that must be maintained between the horn and anvil, as well as the related components for clamping and aligning the film strips in the compression zone defined by those members. Needless to say, the maintenance of such equipment is greater since the normal wear and tear on the equipment would pose a problem in keeping the equipment properly aligned.
Splicers have been developed which employ a small area of contact between a transducer horn member and an anvil member. However, the design and mode of operations of such splicers have been found to result in excessive wear to the ultrasonic work surfaces, especially to the horn.
Many prior art splicers also require that the emulsion and/or an antistatic coating on a photographic film be first scraped off before splicing, especially in the case of polyester films, including those having conventional emulsions.
Among the distinct advantages and features of the present invention is the provision of an ultrasonic film splicer of a design simplicity such that it can be economically manufactured and is inexpensive to operate and maintain. It has been found that the present splicer requires less power input for operation for a given splicing operation; requires less time to achieve a commercially acceptable splice, avoids burning or overheating of the film whereby warping and its related problems are avoided; avoids excessive application of pressure to the film in a manner whereby such pressure can be readily controlled, allows exceptionally accurate alignment of film strips to be spliced, produces a relatively opaque smooth narrow integral splice which avoids interference with the film sound track, fogging of unexposed film adjacent the splicer area, and flow of material into the perforated film (as well as avoids weakening of the small width of film on the outside edge of the perforation; is small and compact; is easy to maintain; can be employed with divergent films of various thicknesses and widths; is easy to operate, particularly in a darkroom; does not require scraping off of the film emulsion (thereby avoiding a dust problem); and greatly minimizes scratching of the film strips in their handling as well as scratching of the film in the splicing zone. The net result is a superior spliced film free of impairment to its structure, photographic characteristics, or sound track. Moreover, film wastage is essentially eliminated due to the superiority of a splice made pursuant to the present method whereby film need not be cut out due to unsuccessful film splices. These and other distinct advantages and features of the present invention will become apparent to one skilled in the art in light of the following detailed description of the preferred embodiments of the present invention.